/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import static com.google.common.collect.Multisets.setCountImpl;

import com.google.common.annotations.GwtCompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.errorprone.annotations.concurrent.LazyInit;
import com.google.j2objc.annotations.WeakOuter;

import java.util.AbstractCollection;
import java.util.Collection;
import java.util.Iterator;
import java.util.Set;
import javax.annotation.CheckForNull;

import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * This class provides a skeletal implementation of the {@link Multiset} interface. A new multiset
 * implementation can be created easily by extending this class and implementing the {@link
 * Multiset#entrySet()} method, plus optionally overriding {@link #add(Object, int)} and {@link
 * #remove(Object, int)} to enable modifications to the multiset.
 *
 * <p>The {@link #count} and {@link #size} implementations all iterate across the set returned by
 * {@link Multiset#entrySet()}, as do many methods acting on the set returned by {@link
 * #elementSet()}. Override those methods for better performance.
 *
 * @author Kevin Bourrillion
 * @author Louis Wasserman
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
abstract class AbstractMultiset<E extends @Nullable Object> extends AbstractCollection<E>
        implements Multiset<E>
{
    // Query Operations

    @Override
    public boolean isEmpty()
    {
        return entrySet().isEmpty();
    }

    @Override
    public boolean contains(@CheckForNull Object element)
    {
        return count(element) > 0;
    }

    // Modification Operations
    @CanIgnoreReturnValue
    @Override
    public final boolean add(@ParametricNullness E element)
    {
        add(element, 1);
        return true;
    }

    @CanIgnoreReturnValue
    @Override
    public int add(@ParametricNullness E element, int occurrences)
    {
        throw new UnsupportedOperationException();
    }

    @CanIgnoreReturnValue
    @Override
    public final boolean remove(@CheckForNull Object element)
    {
        return remove(element, 1) > 0;
    }

    @CanIgnoreReturnValue
    @Override
    public int remove(@CheckForNull Object element, int occurrences)
    {
        throw new UnsupportedOperationException();
    }

    @CanIgnoreReturnValue
    @Override
    public int setCount(@ParametricNullness E element, int count)
    {
        return setCountImpl(this, element, count);
    }

    @CanIgnoreReturnValue
    @Override
    public boolean setCount(@ParametricNullness E element, int oldCount, int newCount)
    {
        return setCountImpl(this, element, oldCount, newCount);
    }

    // Bulk Operations

    /**
     * {@inheritDoc}
     *
     * <p>This implementation is highly efficient when {@code elementsToAdd} is itself a {@link
     * Multiset}.
     */
    @CanIgnoreReturnValue
    @Override
    public final boolean addAll(Collection<? extends E> elementsToAdd)
    {
        return Multisets.addAllImpl(this, elementsToAdd);
    }

    @CanIgnoreReturnValue
    @Override
    public final boolean removeAll(Collection<?> elementsToRemove)
    {
        return Multisets.removeAllImpl(this, elementsToRemove);
    }

    @CanIgnoreReturnValue
    @Override
    public final boolean retainAll(Collection<?> elementsToRetain)
    {
        return Multisets.retainAllImpl(this, elementsToRetain);
    }

    @Override
    public abstract void clear();

    // Views

    @LazyInit
    @CheckForNull
    private transient Set<E> elementSet;

    @Override
    public Set<E> elementSet()
    {
        Set<E> result = elementSet;
        if (result == null)
        {
            elementSet = result = createElementSet();
        }
        return result;
    }

    /**
     * Creates a new instance of this multiset's element set, which will be returned by {@link
     * #elementSet()}.
     */
    Set<E> createElementSet()
    {
        return new ElementSet();
    }

    @WeakOuter
    class ElementSet extends Multisets.ElementSet<E>
    {
        @Override
        Multiset<E> multiset()
        {
            return AbstractMultiset.this;
        }

        @Override
        public Iterator<E> iterator()
        {
            return elementIterator();
        }
    }

    abstract Iterator<E> elementIterator();

    @LazyInit
    @CheckForNull
    private transient Set<Entry<E>> entrySet;

    @Override
    public Set<Entry<E>> entrySet()
    {
        Set<Entry<E>> result = entrySet;
        if (result == null)
        {
            entrySet = result = createEntrySet();
        }
        return result;
    }

    @WeakOuter
    class EntrySet extends Multisets.EntrySet<E>
    {
        @Override
        Multiset<E> multiset()
        {
            return AbstractMultiset.this;
        }

        @Override
        public Iterator<Entry<E>> iterator()
        {
            return entryIterator();
        }

        @Override
        public int size()
        {
            return distinctElements();
        }
    }

    Set<Entry<E>> createEntrySet()
    {
        return new EntrySet();
    }

    abstract Iterator<Entry<E>> entryIterator();

    abstract int distinctElements();

    // Object methods

    /**
     * {@inheritDoc}
     *
     * <p>This implementation returns {@code true} if {@code object} is a multiset of the same size
     * and if, for each element, the two multisets have the same count.
     */
    @Override
    public final boolean equals(@CheckForNull Object object)
    {
        return Multisets.equalsImpl(this, object);
    }

    /**
     * {@inheritDoc}
     *
     * <p>This implementation returns the hash code of {@link Multiset#entrySet()}.
     */
    @Override
    public final int hashCode()
    {
        return entrySet().hashCode();
    }

    /**
     * {@inheritDoc}
     *
     * <p>This implementation returns the result of invoking {@code toString} on {@link
     * Multiset#entrySet()}.
     */
    @Override
    public final String toString()
    {
        return entrySet().toString();
    }
}
